The present invention relates to aircraft control systems and specifically to a flight control system which automatically commands a unique blend of direct lift and conventional longitudinal control such that rapid and precise control of the aircraft flight path is obtained.
Military fighter aircraft, such as the F-16, have special demands imposed upon their control systems which are dictated by the particular combat missions they face.
This includes both the large-scale offensive and defensive air combat maneuvering and precision air-to-air tracking. The blending of longitudinal modes must enable the pilot to easily and effectively accomplish both of these distinctively different tasks with longitudinal control inputs via only the basic aircraft controls.
What is needed is a flight control system that will allow the pilot to use his conventional aircraft control instruments, but for aerial combat, the longitudinal control signals must result in precise flight path control, minimizing the change in aircraft angle of attack by either pilot maneuvering or atmospheric turbulence.
This task has been alleviated, to some degree, by prior art technique and devices that provide numerous aircraft control systems. The extent of these prior art devices is given by the following patents:
U.S. Pat. Nos. 4,093,158 issued on June 6, 1978 to Clews et al, 4,093,159 issued on June 6, 1978 to Gilson, 4,261,537 issued on Apr. 14, 1981 to Tisdale, Sr. et al, and 4,326,253 issued on Apr. 20, 1982 to Cooper et al.
The Clews patent discloses an aircraft control system ultilizing either a first signal which is a function of airspeed or a second signal which is a function of lift. However, the function of the control system is principally directed towards control of aircraft velocity, such that airspeed is maintained at pre-set values. In aerial combat the key objective is maintenance of precise air-to-air tracking, of which airspeed is a secondary factor. Other factors of weapon line stabilization include minimization of gust disturbance and stability of pitch axis angles, which are not addressed by the Clews patent.
The Gilson patent discloses an aircraft control system utilizing altixeter signals as well as lift signals. Like Clews, Gilson presents another partial solution to the present problem by designing a control system principally concerned with the aircraft angle of attack. As mentioned above, the pitch angle is but one concern in aerial combat and the Gilson device is principally a "stall avoidance" system for safety and is inadequate as an aerial combat control device.
The patent of Tisdale, Sr. et al discloses a control system which employs direct lift control with elevator control to control flight path angle. The Tisdale device is superior, for our purposes, to those of Clews and Gilson, in that it provides a means of controlling the flight path angle of aircraft with short term flight path stabilization against environmental disturbances. However, while the Tisdale device provides control of pitch attitude, it remains inadequate for our air-to-air tracking purposes in that it lacks adequate command of longitudinal control which is also needed for combat targeting.
Finally, the patent of Cooper et al discloses a flight control system containing angle of attack, altitude, acceleration, and lift signals. However, like Gilson, Cooper is principally of benefit for safety purposes since it generates a reference angle of attack as a function of vertical velocity such that stall conditions may be avoided and by optimizing an aircraft climb-out performance. The Cooper device is unsuited for our purposes.
In view of the foregoing discussion it is apparent that there currently exists a need for a flight control system that will minimize the effects of atmospheric turbulance and provide rapid and precise control of an aircraft flight path including stability of both pitch attitude and longitudinal control. The present invention is directed towards satisfying that need.